This invention relates to methods of producing a unique composition of glycerol-based polyol products. The unique glycerol-based polyol products include branched, cyclic polyols and a beneficial co-product lactic acid and/or lactate salt as an anti-biodegrading agent. Glycerol-based polyols include polyglycerols, polyglycerol derivatives and a polymer consisting of glycerol units and at least another monomer units to other multiple monomers units. The molecular weight of glycerol-based polyols produced through the improved methods can be preferentially high but also can be low as needed.
Glycidol-based synthesis is particularly useful in producing structured or hyperbranched polyglycerols (HBPG) and high molecular weight HBPG, such as those described in U.S. Pat. No. 6,822,068 B2 and US Published Application 2008/282579 A1. Unfortunately these syntheses rely on expensive monomer glycidol which is often so expensive that in many cases their use on an industrial scale is cost prohibitive.
A number of production processes have been developed for synthesis of glycerol-based polyols, particularly polyglycerols, from inexpensive monomer glycerol. However, these syntheses are mostly limited to producing linear or at least mostly linear, low molecular weight polyglycerols (or oligoglycerols). U.S. Pat. No. 2,258,892 describes various reaction conditions for synthesizing polyglycerols at reaction temperature 200 to 260 degrees Celsius employing 1% of a caustic or salt by weight as the catalyst relative to glycerol used, but only oligomeric polyglycerol products were produced (mean molecular weight: 116 to 314 Daltons). In U.S. Pat. No. 5,641,816 0.12% of LiOH or lithium soaps under nitrogen atmosphere were used. In U.S. Pat. No. 6,620,904 B2 0.1% of calcium hydroxide under vacuum was used. In WO 2007/049950 A2 1% of a weak acid alkaline metal salt was used. In each of these cases, however, only oligomeric polyglycerols were produced.
Another strategy used in the prior art is the use of small amounts of strong bases. In EP 0719752 B1 1% of sodium hydroxide under vacuum or nitrogen was used. JP 3717193 describes using 0.5% of sodium hydroxide under nitrogen. US Application 2008/306211 A1 describes using 0.3% or 0.4% of KOH. Again however the only major product was oligomeric polyglycerols or olygomeric glycerol-based polyols. Other methods are described in U.S. Pat. Nos. 3,637,774, 4,551,561, and 5,198,532, Chinese Patent Application CN 101186696A and Scientific Article Determination of the Optimum Conditions for the Condensation of Glycerin in the Presence of Potassium Hydroxide, D. A. Zhukov, et al., Zhumal Prikladoni Khimii, Vol. 57, No. 2, pp. 389-392 (1984). Unfortunately these methods also only produce linear polyglycerols with no branching or cyclized structures.
Although glycerol is not expensive, the current processes for the glycerol-based condensation polymerizations are often inefficient. The resulting polyols are linear and often have rather low molecular weights, mostly less than 1000 Daltons. In addition these prior art methods lack any anti-biodegrading agents. Thus there is a clear need for and utility in an improved method of synthesizing polyglycerols and other glycerol-based polyols. The art described in this section is not intended to constitute an admission that any patent, publication or other information referred to herein is “prior art” with respect to this invention, unless specifically designated as such. In addition, this section should not be construed to mean that a search has been made or that no other pertinent information as defined in 37 C.F.R. §1.56(a) exists.